Generally, a certain amount of exhaust gas or fuel-air mixture leaks into the crankcase from the combustion chamber while an engine is running. As a result, engine oil is affected by heat, moisture in the combustion gas, fuel and the like to be thinned or degenerated, thereby leaving sludge therein. In order to prevent this phenomenon, a ventilation device called breather has been installed in the crankcase to discharge the gas to the atmosphere. In the gas, a large amount of hydrocarbons (HC) are included, such that a positive crankcase ventilation (PCV) valve is provided to induce the gas again into the combustion chamber for further combustion thereof.
To deal with oil in blow-by gas, a conventional cylinder head cover generally includes an inner bottom surface with a plurality of ribs in a complex labyrinthine fashion. When dense and thick blow-by gas passes the ribs, relatively heavy oil is separated and the blow-by gas separated from the oil flows towards the PCV valve. The oil is directed to an oil pan along an oil line, while the blow-by gas, having passed the PCV valve, is introduced to the combustion chamber for re-burning.
However, there is a problem in such devices in that a multitude of labyrinths are formed at an inner bottom side of the cylinder head cover. Although relatively large oil droplets can be separated due to their weight, oil mist of minute particles are still mixed with the blow-by gas to be re-induced into and burnt in the combustion chamber. Such mist in the blow-by gas has disadvantageous effects on oil consumption and emission sides.